Dissertação (mestrado)—Universidade de Brasília, Instituto de Física, Programa de Pós-Graduação em Física, 2015. / Nanopartículas multicomponentes magnéticas/metálicas tem atraído muito atenção devido as suas propriedades magnéticas e ópticas únicas. Essas heteroestruturas podem ser aplicadas em terapia biomedicinal e imagem ou podem ser utilizadas também como carregadores de droga. Neste trabalho foram preparadas nanopartículas multicomponentes de CoFe 2O4/Ag atrav és do método de Tollens. A síntese de nanopartículas de ferrita de cobalto (CoFe 2O4) foi feita pelo método de co-precipitação química, usando como bases precipitantes, metilamina (CH3NH2) e o hidróxido de sódio (NaOH). Posteriormente as nanopartículas magnéticas foram colocadas em solução contendo o complexo diaminprata e deixadas sob agitação por um determinado tempo. Por _m, este complexo foi reduzido à prata metálica por glicose. Os diâmetros das ferritas puras e das estruturas multicomponentes foram obtidos por meio de difração de raios x do pó. A análise estrutural revelou a formação de única fase cristalina para as nanopartículas de ferrita de cobalto. Para os nanocompósitos multicomponentes o padrão de DRX mostrou a presença de picos de difração correspondentes as estruturas cúbicas das ferritas e da prata. Foi observado que a intensidade dos picos de difração das partículas híbridas tem dependência da razão Ag=CoFe2O4: Do ponto de vista macroscópico, ao serem submetidas a um imã as nanopartículas multicomponentes foram atraídas pelo mesmo, con_rmando assim, o seu comportamento magnético. As medidas de microscopia eletrônica de transmissão (MET) com espectroscopia de energia dispersiva (EDS) possibilitaram a visualização da interação entre as superfícies das duas estruturas. Foi possível através desta técnica obter a composição qualitativa e quantitativa dos materiais em regiões específicas. / Magnetic/metallic nanoparticles multicomponent has attracted much attention due to their unique magnetic and optical properties. Such heterostructures can be applied to biomedicinal therapy or image and can also be used as drug carriers. In this work, multicomponent nanoparticles CoFe2O4/Ag were prepared by Tollens method. The synthesis of cobalt ferrite CoFe2O4 nanoparticles were made by chemical coprecipitation method and, as precipitating bases, we have used methylamine (CH3NH2) and sodium hydroxide (NaOH). Subsequently, the magnetic nanoparticles were placed in the solution containing the complex diamin silver and left stirring for a certain time. Finally, this complex is reduced to metallic silver by glucose The diameters of cobalt ferrite nanoparticles and multicomponent structures were obtained from the powder diffraction X-rays patterns. Structural analysis showed the single spinel phase for ferrites. For the hybrid nanocomposites, the XRD patterns showed the presence of peaks corresponding to the cubic structure of ferrite and silver. It was observed that the intensity of the diffraction peaks of multicomponent particles is ratio dependent. From a macroscopic point of view, the hybrid particles have been subjected to an external magnetic field and were attracted confirming the magnetic behavior. Transmission electron microscopy (TEM) measurements with energy dispersive spectroscopy (EDS) allowed the visualization of both silver and ferrite structure. It was possible with this technique to obtain qualitative and quantitative materials analysis in specific spots.

Detection and identification of pesticide residues on objects of cultural heritage is a serious and urgent challenge that currently faces many museums, Native American communities, and private collections worldwide. Organic artifact materials, such as wood, animal hide, basketry, textiles, paper, horn and bone, have traditionally been treated with pesticides to eradicate and prevent infestation by insects, rodents, and mold. These poisonous substances can persist for years in the controlled environment of a museum storeroom and present a potential poisoning risk to people who come in contact with the objects. Surface-enhanced Raman spectroscopy (SERS) has the potential to detect volatile organic pesticides in this context. The technique can overcome the insensitivity of normal Raman spectroscopy and fluorescence interference, and make possible detection of many organic compounds in parts per million concentration. This investigation is aimed at evaluating SERS for the detection and identification of volatiles in museums, with emphasis on naphthalene vapor. The potential of several SERS-active materials; Tollens mirrors, gold film over nanosphere arrays, citrate-stabilized colloidal silver, and nanoporous gold; to detect Rhodamine B and naphthalene is investigated. The research also highlights the mechanisms that underlie SERS, and the relationship between substrate nanostructure and SERS performance.

© Springer Science+Business Media Dordrecht 2016 / Reducing AgNO3 by glucose at basic pH coated the surface of silica spheres with a high density of hemispherical silver nanoparticles (average diameter 3.2±1 nm). A much lower silver concentration than is standard favored heterogeneous nucleation of silver on the silica surface at the expense of homogeneous nucleation in solution. The slow growth rate of the nuclei promoted the formation of discrete silver particles rather than a continuous shell. Based on scanning electron microscopy and transmission electron microscopy, the surface coverage of silver seed particles was as high as 25% at 10 °C without prior functionalization of the silica. The particles were composed of metallic silver based on x-ray photoelectron spectroscopy. There was a sharp increase in the silver surface coverage and decrease in the particle size when the temperature was raised from 5 °C to 10 °C and the amount of silica was decreased from 0.2 to 0.025 V/V. The size was controlled by the diffusion barrier through the ion shell surrounding the silica spheres and by maintaining reaction conditions where the particles on the surface compete for silver.